Imaging superconductivity under high pressure using NV centers in diamond

Extreme pressure reveals novel quantum phases, including superconductors with record-breaking critical temperatures. These conditions are created in a diamond anvil cell (DAC), which can easily create pressures exceeding 100 GPa equivalent to one million atmospheres. However, detecting superconductivity in a DAC is challenging due to experimental constraints and the very small sample volume.
This difficulty can be circumvented by using optical detection of the magnetic resonance of diamond NV centers. Implanted on the surface of an anvil, these point defects allow for imaging of the magnetic field generated by the sample thus providing direct observation of the Meissner effect. I will describe the operation of NV centers and the influence of stress on their electron spin resonance, demonstrating that maintaining hydrostatic compression is crucial for preserving their unique sensitivity to magnetic fields.
I will detail how NV-center magnetic imaging can be applied to the study of superconductivity in different types of samples. Finally, I will discuss a development of this approach aimed at probing the interior of the superconductor, beyond the mere visualization of the Meissner effect.